Chaotic digital code-division multiple access (CDMA) communication systems

• US 6,331,974 B1
• Filed: 06/23/1998
• Issued: 12/18/2001
• Est. Priority Date: 06/23/1997
• Status: Expired due to Term

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Yang, Tao, Chua, Leon O.
• Primary Examiner(s): VINCENT, DAVID ROBERT
• Application Number:
  US09/103,044
• Time in Patent Office: 1,274 Days
• Field of Search: 370/203, 370/204-209, 370/320, 370/335, 370/342, 370/441, 375/130, 375/131, 375/140, 375/295, 375/316
• US Class Current: 370/342
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 13/0003 Code application, i.e. aspects relating to how codes are applied to form multiplexed channels
• CPC Class Codes: H04J 13/0018 Chaotic
• CPC Class Codes: H04L 27/001 using chaotic signals for secret or secure communication H04L9/001
• CPC Class Codes: H04L 5/02 Channels characterised by the type of signal

Abstract

In the present invention, the structure, principle and framework of chaotic digital code-division multiple access ((CD)²MA) communication systems are presented. Unlike the existing CDMA systems, (CD)²MA systems use continuous pseudo-random time series to spread the spectrum of message signal and the spread signal is then directly sent through channel to the receiver. In this sense, the carrier used in (CD)²MA is a continuous pseudo-random signal instead of a single tone as used in CDMA. The statistical properties of the noise-like carriers are given. In a (CD)²MA system, every mobile station has the same structure and parameters, only different initial conditions are assigned to different mobile stations. Instead of synchronizing two binary pseudo-random sequences as in CDMA systems, an impulsive control scheme is used to synchronize two chaotic systems in (CD)²MA. Simulation results show that the channel capacity of (CD)²MA is at least twice as large than that of CDMA.

Claims

1. A method of modulating a code-division multiple access device that receives information to be transmitted from a selected device, said method comprising the steps of:

a. chaotically generating a seed signal;

b. spreading the spectrum of said seed signal of step a. to generate a spread spectrum signal; and

c. modulating said spread spectrum signal from step b. with said information to be transmitted.

2. A method of modulating a code-division multiple access device as in claim 1 wherein step c. includes the steps of:

d. digitizing said information to be transmitted; and

e. modulating said spread spectrum signal from step b. with said digitized information from step d.

3. A method of modulating a code-division multiple access device as in claim 1 further including the step of:

d. scrambling said spread spectrum signal prior to step c.

4. A method of modulating a code-division multiple access device as in claim 1 further including the step of:

d. preceding step a., randomly selecting and applying initial conditions to a chaotic circuit to generate said seed signal.

5. A method of modulating a code-division multiple access device as in claim 4 wherein said chaotic circuit is Chua'"'"'s circuit.

6. A method of modulating a code-division multiple access device as in claim 5 wherein Chua'"'"'s circuit includes a Chua'"'"'s diode and said seed signal is a voltage across said Chua'"'"'s diode that is normalized.

7. A method of communication between first and second code-division multiple access devices that transmit selected information therebetween via a selected medium, said method comprising the steps of:

a. chaotically generating a seed signal;

b. applying said seed signal of step a. to a first spectrum spreading device in said first code-division multiple access device to generate a first spread spectrum signal in said first code-division multiple access device;

c. modulating said first spread spectrum signal from step b. with said information to be transmitted by said first code-division multiple access device;

d. applying said modulated signal of step c. to said medium for transmission to said second code-division multiple access device;

e. applying said seed signal of step a. to a second spectrum spreading device in said second code-division multiple access device to generate a second spread spectrum signal in said second code-division multiple access device;

f. multiplying said modulated signal received from said medium of step d. together with said second spread spectrum signal of step e. to create a combined signal; and

g. demodulating said combined signal of step f. to generate a recovered information signal.

8. A method of communication between first and second code-division multiple access devices as in claim 7 wherein step c. includes the steps of:

h. digitizing said information to be transmitted; and

i. modulating said first spread spectrum signal from step b. with said digitized information from step h.

9. A method of communication between first and second code-division multiple access devices as in claim 7 further including the steps of:

h. scrambling said first spread spectrum signal prior to step c. with a selected key signal; and

i. scrambling said second spread spectrum signal prior to step f. with said selected key signal.

10. A method of communication between first and second code-division multiple access devices as in claim 7 wherein step f. includes the steps of:

h. filtering said modulated signal from said medium to remove transmission noise from said modulated signal; and

i. multiplying said filtered modulation signal from step h. together with said second spread spectrum signal of step e. to create said combined signal.

11. A method of communication between first and second code-division multiple access devices as in claim 7, preceding step a., further including the step of:

h. randomly selecting and applying initial conditions to a chaotic circuit to generate said seed signal.

12. A method of communication between first and second code-division multiple access devices as in claim 11 wherein:

there is a first chaotic circuit associated with said first code-division multiple access device and a second chaotic circuit associated with said second code-division multiple access device with said randomly selected initial conditions being applied to each of said first and second chaotic circuits; and

said method further includes the step of;

i. applying impulsive synchronization to each of said first and second chaotic circuits at preselected intervals to maintain said first and second spread spectrum signals substantially the same during interaction between said first and second code-division multiple access devices.

13. A method of modulating a code-division multiple access device as in claim 7 or 11 wherein said chaotic circuit is Chua'"'"'s circuit.

14. A method of modulating a code-division multiple access device as in claim 7 or 11 wherein said chaotic circuit is a Chua'"'"'s circuit that includes a Chua'"'"'s diode and said seed signal is a normalized signal of the voltage across said Chua'"'"'s diode.

15. A method of modulating a code-division multiple access device as in claim 12 wherein each of said first and second chaotic circuits is Chua'"'"'s circuit.

16. A method of modulating a code-division multiple access device as in claim 15 wherein each of Chua'"'"'s circuits includes a Chua'"'"'s diode and said seed signal from each of said Chua'"'"'s circuits is a voltage across said Chua'"'"'s diode that is normalized.

17. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 further includes the repetition of all of the recited steps for transmitting information from said second code-division multiple access device to said first code-division multiple access device.

18. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 wherein:

said medium is ether;

step d. includes the step of applying said modulated signal to a first antenna for radiation through said ether; and

said method, prior to step f., further includes the step of receiving said modulated signal from said ether with a second antenna.

19. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 wherein:

said medium is a wire cable;

step d. includes the step of applying said modulated signal to said wire cable through an appropriate first connector; and

said method, prior to step f., further includes the step of receiving said modulated signal from said wire cable through an appropriate second connector.

20. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 wherein:

said medium is a fiber optic cable;

step d. includes the steps of;

converting said modulated signal to a modulated light signal; and

applying said modulated light signal to said fiber optic cable; and

said method, prior to step f., further includes the steps of;

receiving said modulated light signal from said fiber optic cable; and

converting said modulated light signal to a modulated electronic signal.

21. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 wherein:

said medium is a liquid;

step d. includes the steps of;

applying said modulated signal to a first acoustic transducer to generate a modulated acoustic signal; and

applying said acoustic signal from said first acoustic transducer to said liquid; and

said method, prior to step f., further includes the steps of;

receiving said modulated acoustic signal from said liquid with a second acoustic transducer; and

converting said modulated acoustic signal with said second acoustic transducer to a modulated electronic signal.

22. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 wherein:

said medium is a solid material;

step d. includes the steps of;

converting said modulated signal to a modulated ultrasonic signal; and

applying said modulated ultrasonic signal to said solid material; and

said method, prior to step f., further includes the steps of;

receiving said modulated ultrasonic signal from said solid material; and

converting said modulated ultrasonic signal to an electronic modulated signal.

23. A method of communication between first and second code-division multiple access devices as in any one of claims 7-12 wherein:

said medium is an optical system;

step d. includes the steps of;

applying said modulated signal to a light source having a selected bandwidth to generate a modulated optical signal; and

applying said modulated optical signal from said light source to said optical system; and

said method, prior to step f., further includes the steps of;

receiving said modulated optical signal from said optical system; and

converting said modulated optical signal receive from said optical system to an electronic modulated signal.

24. A code-division multiple access device to transmit and receive selected information to and from other code-division multiple access devices, said code-division multiple access device comprising:

a processor coupled to each component of said code-division multiple access device to control the transmit and receive operations thereof;

a message interface disposed to process a message signal for transmission and to provide a received message signal to and from a message source;

a spectrum spreading device disposed to receive a chaotic seed signal to control the generation of a carrier signal;

an input/output transducer disposed to deliver a message signal to a selected transmission medium for transmission to a second code-division multiple access device or to receive a message signal from said selected medium that was transmitted from a second code-division multiple access device;

a multiplier coupled to said spectrum spreading device, said message interface, and said input/output transducer to modulate said carrier signal with said message signal with the modulated signal applied to said input/output transducer in a transmit mode, and to multiply said received message signal from said input/output transducer with said carrier signal to create a received product signal in a receive mode; and

a demodulator coupled between said multiplier and said message interface to demodulate said received product signal to create said received message signal that is delivered to said message interface.

25. A code-division multiple access device as in claim 24 wherein said message interface includes a digital encoder/decoder to digitally encode a message for transmission as said message signal and to decode said received message signal.

26. A code-division access device as in claim 25 wherein said digital encoder/decoder includes an analog to digital converter to encode said message as said message signal, and a digital to analog converter to decode said received message signal.

27. A code-division access device as in claim 24 further includes a key signal generator couple to said spectrum spreading device to scramble said carrier signal using a preselected code.

28. A code-division access device as in claim 24 wherein said chaotic seed signal is generated by chaotic circuit having the same preselected initial conditions as assigned to said second code-division multiple access device with which communication is established.

29. A code-division multiple access device as in claim 28 wherein said chaotic circuit is Chua'"'"'s circuit.

30. A code-division multiple access device as in claim 29 wherein Chua'"'"'s circuit includes a Chua'"'"'s diode and said seed signal is a voltage across said Chua'"'"'s diode that is normalized.

31. A code-division multiple access device as in claim 24 further including a noise filter coupled to said input/output transducer and said multiplier to filter said received message signal before being applied to said multiplier.

32. A code-division multiple access communication system comprising:

a chaotic device to generate a chaotic seed signal;

a selected transmission medium;

a first code-division multiple access device;

a second code division multiple access device;

wherein each of said first and second code-division multiple access devices are disposed to transmit and receive selected information between each other, and each includes;

a processor coupled to each component of said code-division multiple access device to control the transmit and receive operations thereof;

a message interface disposed to process a message signal for transmission and to provide a received message signal to and from a message source;

a spectrum spreading device disposed to receive said chaotic seed signal to control the generation of a carrier signal;

an input/output transducer disposed to deliver a message signal to said selected transmission medium for transmission to another code-division multiple access device or to receive a message signal from said selected transmission medium that was transmitted from another code-division multiple access device;

a multiplier coupled to said spectrum spreading device, said message interface, and said input/output transducer to modulate said carrier signal with said message signal with the modulated signal applied to said input/output transducer in a transmit mode, and to multiply said received message signal from said input/output transducer with said carrier signal to create a received product signal in a receive mode; and

a demodulator coupled between said multiplier and said message interface to demodulate said received product signal to create said received message signal that is delivered to said message interface.

33. A code-division multiple access communication system as in claim 32 wherein said message interface includes a digital encoder/decoder to digitally encode a message for transmission as said message signal and to decode said received message signal.

34. A code-division multiple access communication system as in claim 33 wherein said digital encoder/decoder includes an analog to digital converter to encode said message as said message signal, and a digital to analog converter to decode said received message signal.

35. A code-division multiple access communication system as in claim 32 wherein each of said first and second code-division multiple access devices further includes a key signal generator coupled to said spectrum spreading device to scramble said carrier signal each using a matching preselected code.

36. A code-division multiple access communication system as in claim 32 wherein said chaotic device includes a first chaotic circuit coupled to said first code-division multiple access device and a second chaotic circuit coupled to said second code-division multiple access device with both said first and second chaotic circuits having the same preselected initial conditions.

37. A code-division multiple access communication system as in claim 36 wherein each of said first and second chaotic circuit is a Chua'"'"'s circuit.

38. A code-division multiple access communication system as in claim 37 wherein Chua'"'"'s circuit includes a Chua'"'"'s diode and said seed signal is a voltage across said Chua'"'"'s diode that is normalized.

39. A code-division multiple access communication system as in claim 36 or 37 further includes a synchronization circuit to randomly select and apply said initial conditions to each of said first and second chaotic circuits and to apply impulsive synchronization to each of said first and second chaotic circuits at preselected intervals to maintain said first and second spread spectrum signals substantially the same during interaction between said first and second code-division multiple access devices.

40. A code-division multiple access communication system as in claim 35 further includes a synchronization circuit to randomly select and apply said preselected code to each of said key signal generators.

41. A code-division multiple access communication system as in claim 32 wherein each of said first and second code-division multiple access devices further includes a noise filter coupled to said input/output transducer and said multiplier to filter said received message signal before being applied to said multiplier.

42. A code-division multiple access communication system as in any one of claims 32-41 wherein:

said medium is ether; and

said input/output transducer in each of said first and second code-division multiple access devices is an antenna to apply said modulated signal to, and receive a radiated signal from, said ether.

43. A code-division multiple access communication system as in any one of claims 32-41 wherein:

said medium is a wire cable; and

said input/output transducer in each of said first and second code-division multiple access device includes an appropriate connector to apply said modulated signal to, and receive a signal from, said wire cable.

44. A code-division multiple access communication system as in any one of claims 32-41 wherein:

said medium is a fiber optic cable; and

said input/output transducer in each of said first and second code-division multiple access device includes an electric/optical converter to convert said modulated signal to a modulated light signal for application of a modulated light signal to said fiber optic cable, and to convert said modulated light signal received from said fiber otic cable to a modulated electronic signal.

45. A code-division multiple access communication system as in any one of claims 32-41 wherein:

said medium is a liquid; and

said input/output transducer in each of said first and second code-division multiple access device includes an acoustic transducer to convert said modulated signal to a modulated acoustic signal for application to said liquid, and to convert said modulated acoustic signal received from said liquid to a modulated electronic signal.

46. A code-division multiple access communication system as in any one of claims 32-41 wherein:

said medium is a solid material; and

said input/output transducer in each of said first and second code-division multiple access device includes an ultrasonic transducer to convert said modulated signal to a modulated ultrasonic signal for application to said solid material, and to convert said modulated ultrasonic signal received from said solid material to a modulated electronic signal.

47. A code-division multiple access communication system as in any one of claims 32-41 wherein:

said medium is an optical system; and

said input/output transducer in each of said first and second code-division multiple access device includes;

a light source coupled to said optical system;

a light driver coupled to said light source coupled to receive said modulated signal to cause said light source to emit and apply a modulated light beam to said optical system; and

a light detector coupled to said optical system to detect and convert a received modulated light beam from said optical system to said received modulated electronic signal.